Positive Electrode Active Material and Preparing Method Thereof

Abstract

A positive electrode active material includes a lithium transition metal oxide having a nickel content of 70 mol % or greater with respect to all metals excluding lithium, wherein EELS analysis results for a particle surface satisfy Equation 1 below:0.85≤I(854 eV)/I(855.5 eV)<1  [Equation 1]wherein I (854 eV) indicates a peak intensity observed around 854 eV, and I (855.5 eV) indicates a peak intensity observed around 855.5 eV.

What is claimed is: 
     
         1 . A positive electrode active material comprising: a lithium transition metal oxide having a nickel content of 70 mol % or greater with respect to all metals excluding lithium,
 wherein EELS analysis results of a particle surface of the positive electrode active material satisfy Equation 1 below:   
       
         
           
             
               
                 
                   
                     0.85 
                     ≤ 
                     
                       
                         I 
                         ⁡ 
                         ( 
                         
                           854 
                           ⁢ 
                              
                           eV 
                         
                         ) 
                       
                       / 
                       
                         I 
                         ⁡ 
                         ( 
                         
                           8 
                           ⁢ 
                           5 
                           ⁢ 
                           5 
                           .5 
                              
                           eV 
                         
                         ) 
                       
                     
                     < 
                     1 
                   
                 
                 
                   
                     [ 
                     
                       Equation 
                       ⁢ 
                           
                       1 
                     
                     ] 
                   
                 
               
             
           
         
         wherein, 
         I (854 eV) indicates a peak intensity observed around 854 eV, and 
         I (855.5 eV) indicates a peak intensity observed around 855.5 eV. 
       
     
     
         2 . The positive electrode active material of  claim 1 , wherein a molar ratio of lithium to all metal elements excluding lithium in the lithium transition metal oxide is from 1.01 to 1.09. 
     
     
         3 . The positive electrode active material of  claim 1 , wherein the lithium transition metal oxide is represented by Formula 1 below:
   Li a Ni b Co c Mn d Q e O 2+f   [Formula 1]
   wherein,   a, b, c, d, e, and f satisfy 1.03≤a≤1.09, 0.7≤b<1.0, 0<c<0.3, 0<d<0.3, 0≤e<0.1, b+c+d+e=1, and −0.1≤f≤1.0, respectively, and   Q is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.   
     
     
         4 . The positive electrode active material of  claim 1 , wherein the positive electrode active material has a D 50  of 8 μm to 15 μm. 
     
     
         5 . A method for preparing a positive electrode active material of  claim 1 , comprising:
 mixing a precursor having a nickel content of 70 mol % or greater with respect to total moles of transition metal and a lithium source to form a mixture and firing the mixture to prepare a fired body; and   washing the fired body with a washing solution in an amount of 30 parts by weight to 70 parts by weight with respect to 100 parts by weight of the fired body to prepare a lithium transition metal oxide.   
     
     
         6 . The method of  claim 5 , wherein the preparing of the fired body involves mixing the precursor and the lithium source so that Li/M, which is a molar ratio of lithium in the lithium source to total metal elements of the precursor, is from 1.01 to 1.09. 
     
     
         7 . The method of  claim 5 , wherein the washing in the preparing of the lithium transition metal oxide is performed by placing the fired body in water and stirring the mixture at a temperature of 15° C. to 25° C. for 1 minute to 20 minutes at a rate of from 1,500 rpm to 2,500 rpm. 
     
     
         8 . The method of  claim 5 , wherein the firing in the preparing of the fired body is performed at a temperature of from 700° C. to 900° C. 
     
     
         9 . A positive electrode comprising the positive electrode active material of  claim 1 . 
     
     
         10 . A lithium secondary battery comprising the positive electrode of  claim 9 ; a negative electrode containing a negative electrode active material; and an electrolyte.